Method of securing fastener

Abstract

A method for automatically tightening a tapped member such as a nut is disclosed. A socket of an open end air wrench mounted on a nut tightening robot is coupled with the tapped member. The robot rotates the socket in a first direction, i.e., a tightening direction, to a first relatively small torque, and subsequently rotates the socket in a second direction opposite to the first direction to a predetermined position, i.e., a central receptive position after the socket being disengaged from the tapped member. A rotary encoder is provided to generate pulses in response to the rotation of the socket in the second rotational direction. An angle of rotation of this rotation of the socket in the second direction is detected by counting the number of pulses generated by the encoder. In response to the detected angle of rotation a torque wrench is coupled with the tapped member and the robot rotates the torque wrench in the tightening direction to a second relatively great torque.

What is claimed is: 
     
       1. A method of tightening a tapped member, comprising the steps of: coupling first coupling means with the tapped member;   rotating said first coupling means in a first rotational direction to tighten the tapped member to a first predetermined torque when said first coupling means couples with the tapped member;   rotating said first coupling means in a second rotational direction opposite to said first rotational direction after said first coupling means being disengaged from the tapped member and after having tightened the tapped member to said first predetermined torque until said first coupling means takes a predetermined position;   detecting an angle of rotation of said first coupling means in said second rotational direction until said predetermined position and generating a rotational angle indicative signal indicative of said detected angle of rotation;   coupling second coupling means with the tapped member in response to said rotational angle indicative signal; and   rotating said second coupling means in said first rotational direction to tighten the tapped member firmly to a second predetermined torque that is greater than said first predetermined torque.   
     
     
       2. The method as claimed in claim 1, wherein said first mentioned step of coupling includes coupling a socket of an open end air wrench with the tapped member, and said second mentioned coupling step includes coupling a head of a torque wrench with the tapped member. 
     
     
       3. The method as claimed in claim 2, wherein said first mentioned rotating step comprises rotating said first coupling means until said first coupling means attains a central receptive position of said socket. 
     
     
       4. A method of tightening a tapped member, comprising the steps of: coupling first coupling means with the tapped member;   rotating said first coupling means in a first rotational direction to tighten the tapped member to a first predetermined torque when said first coupling means couples with the tapped member;   rotating said first coupling means in a second rotational direction opposite to said first rotational direction after said first coupling means being disengaged from the tapped member after having tightened the tapped member to said first predetermined torque until said first coupling means takes a predetermined position;   detecting an angle of rotation of said first coupling means in said second rotational direction until said predetermined position and generating a rotational angle indicative signal indicative of said detected angle of rotation;   positioning second coupling means in alignment with the tapped member in response to said rotational angle indicative signal;   coupling said second coupling means with the tapped member after having been positioned in alignment with the tapped member; and   rotating said second coupling means in said first rotational direction to tighten the tapped member firmly to a second predetermined torque that is greater than said first predetermined torque.   
     
     
       5. A method of tightening a tapped member, comprising the steps of: coupling first coupling means with the tapped member;   rotating said first coupling means in a first rotational direction to tighten the tapped member to a first predetermined torque when said first coupling means couples with the tapped member;   after having tightened the tapped member to said first predetermined torque, disengaging said first coupling means from the tapped member;   after disengaging said first coupling means from the tapped member, rotating said first coupling means in second rotational direction opposite to said first rotational direction until said first coupling means takes a predetermined position;   detecting an angle of rotation of said first coupling means in said second rotational direction and generating a rotational angle indicative signal indicative of said detected angle of rotation;   coupling second coupling means with the tapped member in response to said rotational angle indicative signal; and   rotating said second coupling means in said first rotational direction to tighten the tapped member firmly to a second predetermined torque that is greater than said first predetermined torque.